The present invention relates to a radiographic imaging system which creates image data of diagnostic images by performing at least one of an exposure field recognition process and trimming process on image data of radiographic images taken of a subject.
As diagnostic images for physicians, radiographic images taken by irradiating a subject (patient) with radiation (X rays, α rays, β rays, γ rays, electron beams, ultraviolet rays, etc.) are widely used. Currently, radiographic imaging systems for medical treatment, which capture a radiographic image, perform image processing and process displaying and so forth digitally, are being put into practical use due to an increased use of CR (computed radiography) and DR (digital radiography) radiographic imaging systems.
A radiographic imaging system comprises, for example, an imaging apparatus which captures a radiographic image of a subject and outputs its digital image data, an image processing apparatus which performs image processing on the radiographic image that was taken, and an image diagnosis apparatus which displays the radiographic image after image processing, etc. These imaging apparatus, image processing apparatus and image diagnosis apparatus are, for example, located in different locations in a hospital, and are connected to each other via a network.
Image data of a radiographic image of a subject taken by the imaging apparatus is output from the imaging apparatus and input into the image processing apparatus via the network, where it undergoes image processing by the image processing apparatus. After that, when a physician is making a diagnosis, image data after image processing is output from the image processing apparatus and input into the image diagnosis apparatus via the network, and displayed on the image diagnosis apparatus. Diagnosis by a physician is performed by looking at diagnostic images displayed on the image diagnosis apparatus.
Incidentally, when taking a radiographic image, if a range of radiation exposure (exposure field) is inappropriately large, a diagnostic image having an image area of an appropriate size is created by performing a trimming process in the image processing apparatus when the image is checked after being taken.
However, since the next radiographic image will be taken with the same inappropriately large range of exposure (if a person taking an image and a person checking an image are different people, it may not be noticed that the range of radiation exposure is inappropriately large), trimming process must be implemented each time an image is checked. There is also a problem that it takes time to process a large image before it is trimmed.
Conversely, if the range of radiation exposure is set to be inappropriately small, there is a problem that if an image region required in diagnosis is not included in the radiographic image after being taken, the image must be retaken, thereby increasing the burden on a patient and reducing trust in a medical facility.
Also, even if the image region is optimally set by trimming process, it is used only during the trimming process, and those results are not used when taking images. As a result, the range of radiation exposure must be separately adjusted each time.
As described above, when taking radiographic images, the range of radiation exposure must be adjusted each time and trimming process of the radiographic image after being taken must be performed each time. As a result, there is a problem that the burden on the technician taking the radiographic images is extremely large.
Also, when it is desired to take images of the same site of the same patient at the same position each time over the course of time, as in follow-up examinations, normally the images are taken while positioning the same imaged site of the patient at the same position, at the same distance and at the same radiation dose.
However, there are cases where imaging at the same position as the previous time is not possible, and the image is taken at a position as close to the same position as possible, due to reasons such as a normally-used radiographic imaging system being unusable for only a certain imaging session, or an inability to twist the patient's body for positioning due to back pain, for example. In this case, the imaged site of the patient may be imaged obliquely in the radiographic images taken at that time, due to the arrangement of a radiation detector or a position of the patient when imaged, etc.
Here, the imaged site of the patient being imaged obliquely (also stated as “image taken with the patient tilted” hereinafter) means that the imaged site of the patient imaged in radiographic images during a certain session is tilted with respect to the same imaged site of the patient in the same position taken in radiographic images taken previously, in the case where it is desired to take images of the same site of the same patient at the same position each time over the course of time, as in follow-up examinations as described above.
When images cannot be taken at the same position as in past images, one may also consider postponing imaging and rotating the imaged site or the radiation detector so that the patient is imaged in the same position.
When trimming a radiographic image taken with the patient tilted (refer to FIG. 7A), one may consider, for example, correcting the tilt by rotating the radiographic image in a direction opposite the tilt so that the patient is straight on (refer to FIG. 7B), and trimming the radiographic image after correction (refer to FIG. 7C). In this case, the trimming process is performed by specifying a rectangular region whose sides extend in a horizontal direction and a vertical direction (dotted line A in FIG. 7C). Therefore, although a size of a trimmed region is nearly the same, there is a problem that image quality is degraded because an interpolation process is performed between pixels by the rotation process.
On the other hand, when trimming a radiographic image taken with the patient tilted (refer to FIG. 8A), one may consider tilting the rectangular trimmed region in the direction of tilt of the patient (rotating the trimmed region around an axis extending in a vertical direction on a display surface of the radiographic image, in accordance with the tilt of the patient) (refer to FIG. 8B). In this case, since rotation of the radiographic image is unnecessary, image quality is not degraded, but it is difficult to specify the region to be trimmed. An actual trimmed region is the smallest rectangular region that includes the tilted trimmed region (dotted line A of FIG. 8C) and whose sides extend in the horizontal direction and vertical direction (solid line B of FIG. 8C), and therefore the trimmed region becomes large.
Prior art references relevant to the present invention are JP 2009-207527 A, JP 2000-333936 A and JP 2005-184750 A.
In JP 2009-207527 A, it is described that in the case where a subject was imaged in the past with the same imaging menu as the current imaging, positions of a radiation tube and a radiation detector and so forth are determined based on information that indicates the most recent position, etc.
In JP 2000-333936 A, it is described that a region outside an exposure field, that is, a region from an edge of a captured image to a side edge of each shielding plate, is determined from position information of each shielding plate of an X-ray aperture and so forth, and a blackening process is performed.
In JP 20005-184750 A, it is described that a relative position of an area of concern for each imaged site is stored, and when imaging the same site, an imaging process is performed using characteristic values of a region corresponding to the relative position.